Question: What is the enrollment of undergraduates at the university that employed the person who declared the American frontier "closed" in 1893?
Context: Document 1: Frederick Jackson Turner: Frederick Jackson Turner (November 14, 1861 – March 14, 1932) was an American historian in the early 20th century, based at the University of Wisconsin until 1910, and then at Harvard. He was primarily known for his “Frontier Thesis.” He trained many PhDs who came to occupy prominent places in the history profession. He promoted interdisciplinary and quantitative methods, often with a focus on the Midwest. He is best known for his essay "The Significance of the Frontier in American History", whose ideas formed the Frontier Thesis. He argued that the moving western frontier shaped American democracy and the American character from the colonial era until 1890. He is also known for his theories of geographical sectionalism. In recent years historians and academics have argued strenuously over Turner's work; all agree that the Frontier Thesis has had an enormous impact on historical scholarship and the American soul.
Document 2: Harvard University: Harvard's 2,400 professors, lecturers, and instructors instruct 7,200 undergraduates and 14,000 graduate students. The school color is crimson, which is also the name of the Harvard sports teams and the daily newspaper, The Harvard Crimson. The color was unofficially adopted (in preference to magenta) by an 1875 vote of the student body, although the association with some form of red can be traced back to 1858, when Charles William Eliot, a young graduate student who would later become Harvard's 21st and longest-serving president (1869–1909), bought red bandanas for his crew so they could more easily be distinguished by spectators at a regatta.
Document 3: Great Plains: The rural Plains have lost a third of their population since 1920. Several hundred thousand square miles (several hundred thousand square kilometers) of the Great Plains have fewer than 6 inhabitants per square mile (2.3 inhabitants per square kilometer)—the density standard Frederick Jackson Turner used to declare the American frontier "closed" in 1893. Many have fewer than 2 inhabitants per square mile (0.77 inhabitants per square kilometer). There are more than 6,000 ghost towns in the state of Kansas alone, according to Kansas historian Daniel Fitzgerald. This problem is often exacerbated by the consolidation of farms and the difficulty of attracting modern industry to the region. In addition, the smaller school-age population has forced the consolidation of school districts and the closure of high schools in some communities. The continuing population loss has led some to suggest that the current use of the drier parts of the Great Plains is not sustainable, and there has been a proposal - the "Buffalo Commons" - to return approximately 139,000 square miles (360,000 km2) of these drier parts to native prairie land.
Answer: 7,200
Reasoning steps: who declated the American frontier "closed" in 1893? Answer: Frederick Jackson Turner
Frederick Jackson Turner >> employer Answer: Harvard
What is the enrollment of undergraduates at Harvard ? Answer: 7,200